1. Field of the Invention
The present invention relates to a method of driving an AC discharge memory-operating type plasma display panel and to a plasma display device in which a plurality of scan electrodes and a plurality of data electrodes are arranged to intersect with each other, discharge is generated at the intersections of the scan electrodes and the data electrodes upon application of a desired data pulse to the data electrodes to effect and screen display.
2. Description of the Related Art
PDP (plasma display panels) generally offer many features, including thin construction, a low level of flicker, a high display contrast ratio, relative ease of application to large screens, and a high response speed. In addition, PDP are self-light emitting and are therefore capable of multicolor emission through the use of phosphors. Due to these features, the use of PDP has been expanding in recent years in the fields of large public display devices and color television.
PDP include the ac-discharge type, in which electrodes are covered by a dielectric, that operates in a state of indirect AC discharge; and the dc discharge type, in which electrodes are exposed in a discharge space, that operates in a direct-current discharge state.
The ac discharge type includes a memory-operating type that uses the memory of a discharge cell; and a refresh-operation type that does not use the memory of a discharge cell. The luminance of both the memory-operating type of PDP and the refresh operation type of PDP is substantially proportional to the number of discharges, i.e., the number of repeated voltage pulses. The refresh operation type of PDP exhibits a decrease in luminance if the display capacitance is increased, and this type of PDP is therefore used in PDP having little display capacitance.
FIG. 1 is a perspective sectional view showing the construction of a display cell in an ac-discharge memory-operating type of PDP. The PDP comprised by: insulating substrates 1 and 2, scan electrodes 3, sustain electrodes 4, bus electrodes 5 and 6, data electrodes 7, discharge gas space 8, phosphor 11, dielectric layer 12, protective layer 13, dielectric layer 14, and barriers 9.
The front surface and back surface, i.e., insulating substrates 1 and 2, are made of glass. Transparent scan electrodes 3 and transparent sustain electrodes 4 are formed on insulating substrate 2. Bus electrodes 5 and 6 are arranged to overlie scan electrodes 3 and sustain electrodes 4 to reduce the electrode resistance. Data electrodes 7 are formed on insulating substrate 1 orthogonal to scan electrodes 3 and sustain electrodes 4. Discharge gas space 8 is the space between insulating substrate 1 and insulating substrate 2 and is filled with a discharge gas that is composed of helium, neon, or xenon, or a compound gas of these gases. Phosphor 11 converts the ultraviolet light that is generated by discharge of the discharge gas to visible light 10. Dielectric layer 12 covers scan electrodes 3 and sustain electrodes 4. Protective layer 13 is a layer made of magnesium oxide or the like and protects dielectric layer 12 from discharge. Dielectric layer 14 covers data electrodes 7. Barriers 9 partition display cells from other adjacent display cells. The surface of data electrodes 7 is covered by dielectric layer 14. A plurality of barriers 9 are provided on the surface of dielectric layer 14. Phosphor 11 is applied to the surface of dielectric layer 14 between adjacent barriers 9 and to the side surfaces of barriers 9.
FIG. 2 is a vertical section of a single display cell in the AC discharge memory-operating type of PDP shown in FIG. 1.
The discharge operation of the selected display cell is next described with reference to FIG. 2. Discharge occurs when a pulse voltage that exceeds a discharge threshold value is applied between scan electrode 3 and data electrode 7. When discharge occurs, the positive and negative charges that are generated by the discharge are absorbed into the surfaces on both sides, i.e., into the surface of dielectric layer 12 and phosphor 11, and charge accumulation takes place according to the polarity of the applied pulse voltage. This charge is hereinbelow referred to as xe2x80x9cbarrier charge.xe2x80x9d The equivalent internal voltage that is generated by the accumulation of this charge at the two ends of discharge gas space 8 (in FIG. 2, above and below the plane of the figure), i.e., barrier voltage, is of the opposite polarity of the pulse voltage. The effective voltage inside the display cell therefore drops with increase in the barrier charge even though the applied pulse voltage is kept at a fixed value. When the effective voltage inside the display cell falls to the extent that discharge can no longer be sustained, discharge ceases. If the polarity of the voltage that is applied to data electrode 7 is reversed at this time, the barrier charge is erased. Since the collision of positive charge of high mass with phosphor 11 shortens the life of the phosphor, a voltage that is positive with respect to scan electrode 4 is applied to data electrode 7 such that negative charge (electrons) of low mass are stored in the surface of phosphor 11. In order to sustain discharge in this state, sustain electrodes 4 are provided parallel to scan electrodes 3, and a sustaining discharge is continued between scan electrodes 3 and sustain electrodes 4. Thus, after discharge between data electrode 7 and scan electrode 4 is initiated in a selected display cell that is to emit light, a sustaining discharge pulse, which is a pulse voltage of the same polarity as the barrier voltage, is applied between adjacent scan electrode 3 and sustain electrode 4, whereby the effective voltage is equivalent to the barrier voltage added to the voltage of the sustaining discharge pulse. The effective voltage therefore exceeds the discharge threshold value even though the voltage of the sustaining discharge pulse is low, and discharge is thus sustained. Discharge is thus sustained through the application of sustaining discharge pulses alternately to scan electrode 3 and sustain electrode 4. This function is the above-described memory function.
The sustain discharge is halted by applying, as an erase pulse, a wide pulse of low voltage or a narrow pulse of approximately the same voltage level as the sustaining discharge pulse to scan electrode 3 or sustain electrode 4 so as to neutralize the barrier voltage.
FIG. 3 is a block diagram showing: a PDP that is formed by arranging display cells such as shown in FIG. 2 in a matrix, a control circuit, a scan driver, a sustain driver, and a data driver.
PDP 15 is a panel for dot matrix display in which mxn display cells 16 are arranged. In PDP 15, scan electrodes X1, X2, . . . , Xm and sustain electrodes Y1, Y2, . . . , Ym arranged parallel to each other are provided as row electrodes; and data electrodes D1, D2, . . . , Dn arranged orthogonal to the row electrodes are provided as column electrodes.
Scan driver 21 applies a voltage of the scan electrode drive waveform to scan electrodes X1, X2, . . . , Xm. Sustain driver 22 applies a voltage of the sustain electrode drive waveform to sustain electrodes Y1, Y2, . . . , Ym. Data driver 50 applies a voltage of the data electrode drive waveform to data electrodes D1, D2, . . . , Dn.
Control circuit 60 generates signals for controlling data driver 50, scan driver 21, and sustain driver 22 based on vertical synchronizing signals Vsync, horizontal synchronizing signals Hsync, clock signals xe2x80x9cClock,xe2x80x9d and display data signals DATA.
Display data signal DATA are signals indicative of the data that are to be displayed in each display cell. Vertical synchronizing signal Vsync is a signal indicative of the period of a frame in which a series of operations is concluded, from a preparatory discharge interval until an erase discharge interval, and the starting point of the frame. In addition, if one frame is made up of a plurality of fields, and each field contains from the preparatory discharge interval up to the sustain discharge interval, the fields may be constituted asynchronous with vertical synchronizing signal Vsync. Vertical synchronizing signal Vsync may also indicate the period and the start point of one field. Although horizontal synchronizing signal Hsync is a signal that designates the start of scanning for each horizontal scanning line in a CRT, in a PDP, it is used as a signal that indicates the timing for taking in display data signal DATA for each horizontal scanning line. Clock signal xe2x80x9cClockxe2x80x9d is a reference clock for transferring display data signals DATA.
The drive method of a PDP with a construction of the foregoing description will described below.
FIG. 4 shows a timing chart of the output waveforms of scan driver 21, sustain driver 22, and data driver 20 of the PDP shown in FIG. 3.
Sustain electrode drive pulse signal Wu is a voltage signal that is applied in common to sustain electrodes Y1, Y2, . . . , Ym. Scan electrode drive pulse signals Ws1, Ws2, . . . , Wsm are voltage signals that are applied to scan electrodes X1, X2, . . . , Xm, respectively. Data electrode drive pulse signal Wd is a voltage signal that is applied to data electrode Di for 1xe2x89xa6ixe2x89xa6n). Driving the PDP involves performing a preparatory discharge interval, a write discharge interval, a sustaining discharge interval, and an erase discharge interval as one period.
The preparatory discharge interval is a time interval for generating barrier charge and activated particles inside the discharge gas space in order to obtain a stable write discharge characteristic in the write discharge interval. A preparatory discharge pulse Pp is first applied to simultaneously discharge all display cells of PDP 15. Preparatory discharge erase pulse Ppe is then applied to all scan electrodes in order to eliminate the charge of the created barrier charge that would interfere with write discharge and sustaining discharge. In other words, preparatory discharge pulse Pp is first applied to scan electrodes X1, X2, . . . , Xm to bring about preparatory discharge in all display cells. Next, the potential of sustain electrodes Y1, Y2, . . . , Ym is raised to the level of sustain voltage Vs, and in addition, preparatory discharge erase pulse Ppe having a potential that gradually drops is applied to scan electrodes X1, X2, . . . , Xm to bring about erase discharge. When erase discharge occurs, the barrier voltage that has accumulated due to preparatory discharge pulse is relaxed. Erasing that is described here refers to either eliminating all barrier charge or adjusting the amount of barrier charge to facilitate subsequent write discharge or sustaining discharge.
The write discharge interval is a time interval for causing selected display cells that are to emit light to discharge, and for creating barrier charge. Scan pulse Pw is successively applied to each of scan electrodes X1, X2, . . . , Xm, and in synchronism with this scan pulse Pw, data pulse Pd is selectively applied to data electrode Di for 1xe2x89xa6ixe2x89xa6n of display cells in which display is to be effected. Write discharge is thus generated and barrier charge created.
The sustaining discharge interval is a time interval for sustaining the discharge of display cells in which barrier charge was generated during the write discharge interval. In order to effect a desired luminance in display cells in which write discharge was effected in a write discharge interval, sustaining discharge pulse Pc is applied to scan electrodes X1, X2, . . . , Xm and sustaining discharge pulse Ps having a phase that is delayed 180 degrees from that of the sustaining discharge pulse Pc is applied to sustain electrodes Y1, Y2, . . . , Ym repeatedly and alternately for a required number of times. The necessary number of sustaining discharges is thus repeated. In this case, the amplitude of scan electrodes X1, X2, . . . , Xm and sustain electrodes Y1, Y2, . . . , Ym is assumed to be Vs. The potential difference between scan electrodes X1, X2, . . . , Xm and sustain electrodes Y1, Y2, . . . , Ym is set such that the voltage obtained by adding the voltage resulting from barrier charge to Vs is a value that exceeds the voltage for initiating discharge.
The erase discharge interval is a time interval for adjusting the amount of barrier charge so as to facilitate subsequent preparatory discharge, write discharge, and sustaining discharge. Erase discharge occurs when erase pulse Pe having a gradually falling potential is applied to scan electrodes X1, X2, , Xm, to erase the barrier charge that has accumulated due to sustaining discharge. Erasing in this case refers to entirely eliminating barrier charge or adjusting the amount of barrier charge so as to facilitate subsequent preparatory discharge, write discharge, or sustaining discharge.
Data pulses Pd are not applied to display cells in which light emission is not desired (GND potential in FIG. 4), and the occurrence of discharge is thus prevented.
A desired image is thus displayed on the PDP by means of the series of operations from preparatory discharge interval to erase discharge interval. In the above-described write discharge interval, data pulse Pd is applied to all data electrodes at the same timing, whereby a light emission current flows in unison for each scan electrode immediately after the application of both scan pulse Pw and data pulse Pd. As a result, there is the problem that, in a case in which the light emission current is large, such as in a PDP having a large display screen, a sufficient voltage characteristic for bringing about write discharge in display cells cannot be obtained due to the voltage drop caused by driver output impedance or the electrode wiring resistance of the PDP. xe2x80x9cElectrode wiringxe2x80x9d refers to scan electrodes 3, sustain electrodes 4, bus electrodes 5, 6, or data electrodes 7. In addition, xe2x80x9celectrode wiring resistance of scan electrodes 3 and sustain electrodes 4xe2x80x9d refers to the resistance between scan electrodes 3 and sustain electrodes 4 on one hand and bus electrodes 5 and 6 on the other.
Not only does a light emission current flow to the electrodes, but a current also flows for charging and discharging the electrostatic capacity between electrodes, and the capacity becomes a load with respect to the application of a drive pulse. Narrowing the picture element pitch or increasing screen size in the interest of raising the degree of detail of the PDP shrinks the distance between electrodes and increases the length of electrode wiring, whereby the electrostatic capacity between electrodes increases, and this current attains a high value. When the current for charging and discharging becomes large, the noise level generated by this current also increases. This noise influences other signals and causes erroneous writing in display cells. This noise is also undesirable in that it is also a source of noise that is radiated to the outside. Furthermore, raising the drive voltage to each driver to compensate for the amount of voltage drop causes light emission of display cells in which light emission is not desired.
The present applicant has already disclosed a method for solving these problems in the publication of Japanese Patent No. 2950270. In this method, the data electrodes are divided into a plurality of data electrode groups (an example is here shown in which the data electrodes are divided into two groups: data electrodes Da1-Daj and data electrodes Db1-Dbk) as shown in FIG. 5, and the phase of the data pulses of a write discharge interval is shifted for each data electrode group.
The signals that are applied to each electrode have the waveforms as shown in FIG. 6. Sustain electrode drive pulse signal Wu is the signal that is applied in common to sustain electrodes Y1, Y2, . . . , Ym. Scan electrode drive pulse signals Ws1, Ws2, . . . , Wsm are the signals that are applied to scan electrodes X1, X2, . . . , Xm, respectively. Data electrode drive pulse signal Wa is the signal that is applied to data electrodes Da1, Da2, . . . , Daj. Data electrode drive pulse signal Wb is the signal that is applied to data electrodes Db1, Db2, . . . , Dbk. One period (one frame) includes a first field and a second field, and the first and second fields are each composed of a preparatory discharge interval, a write discharge interval, and a sustaining discharge interval.
In the write discharge interval of the first field, the pulse width of the data pulses that are applied to data electrodes Da1, Da2, . . . , Daj is the same as the scan cycle, while the data pulses applied to data electrodes Db1, Db2, . . . , Dbk have a narrow pulse width with a start timing delayed by time Td from the start time of the data pulse applied to data electrodes Da1, Da2, . . . , Daj. In the write discharge interval of the second field, however, the data pulses that are applied to data electrodes Da1, Da2, . . . , Daj have a narrow pulse width with a start timing delayed by time Td, while the pulse width of the data pulses that are applied to data electrodes Db1, Db2, . . . , Dbk is the same as the scan period.
Since the start timings of the data pulses to data electrodes Da1, Da2, . . . , Daj and the data pulses to data electrodes Db1, Db2, . . . , Dbk diverge from each other, the timing of the light emission current that flows to scan electrodes X1, X2, . . . , Xm is shifted and the peak value of the light emission current is reduced. Data pulses of the width of scan period are always applied to one of the data electrode groups, and regarding the scan of that data electrode group, the pulse output continues without returning to the reference potential if write discharge occurs in consecutive display cells. The charge that accumulates in the electrostatic capacity between electrodes is therefore not charged and discharged, and power consumption can be reduced.
As another means for solving the above-described problem, the present applicant has disclosed the method described in the publication of Japanese Patent No. 2953342. In this method, the data electrodes are divided into a plurality of data electrode groups (An example is here shown in which the data electrodes are divided between first and second data electrode groups). Signals of the waveforms shown in FIG. 7 are applied to each electrode. Sustain electrode drive pulse signal Wu is the signal that is applied in common to the sustain electrodes. Scan electrode drive pulse signals Ws1, Ws2, . . . , Wsm are the signals that are respectively applied to the m scan electrodes. Data electrode drive pulse signal Wa is the signal that is applied to the data electrodes of the first data electrode group, and data electrode drive pulse signal Wb is the signal that is applied to the data electrodes of the second data electrode group.
The pulse start of data electrode drive pulse signal Wa coincides with the switch timing of the scan period, and the pulse ends before the switch timing of the scan period. The pulse start of data electrode drive pulse signal Wb comes after the switch timing of the scan period, and the pulse end coincides with the switch timing of the scan period.
The peak value of the light emission current is reduced by shifting the timing of the light emission current that flows to each of the scan electrodes for the first data electrode group and the second data electrode group.
With the increased attention on environmental issues in recent years, a decrease of power consumption of all electronic devices has been required. The voltage that is applied to electrodes in a PDP is a high voltage of several hundred volts, and since a PDP has a large number of picture elements, even a slight increase or decrease in the current to each of the electrodes results in a large increase or decrease in the current to the entire PDP. In addition, it is known that the increase in the current heat the PDP, thus decreasing the life of the PDP. Decreasing power consumption by whatever means is therefore a crucial issue in the development of PDP.
One method of decreasing power consumption that can be considered in addition to the methods described in the above-described publications involves delaying the start timing and advancing the end timing of the data pulses to one of the data electrode groups. In this method, however, the shortness of the data pulse width of one of the data electrode groups, i.e., the write pulse width, results in cases of insufficient formation of barrier charge. A display cell in which the barrier charge is insufficiently formed does not easily make the transition to sustaining discharge and may not emit light.
It is an object of the present invention to provide a method of driving an AC discharge memory-operating type plasma display panel, a plasma display device of the kind described at the beginning of this document and that has a low noise level, that suppresses power consumption to a low level, and that has a stable drive voltage.
According to one aspect of the invention, a method of driving a plasma display, comprises the steps of dividing data electrodes into a plurality of data electrode groups, and applying data pulse strings, which are composed of a plurality of consecutive data pulses in which the start timing of the first data pulse is delayed by a predetermined time and the end timing of the last data pulse is advanced by a predetermined time, are applied to data electrodes at a different phase for each data electrode group.
The start timing and the end timing of the data pulses are shifted by the units of the data electrode groups, whereby the combination of the charge/discharge current for charging and discharging the electrostatic capacity between electrodes that accompanies changes in the drive pulse and the light emission current that occurs with discharge can be lowered, thereby decreasing the current peak value, and decreasing noise. Furthermore, because the data pulse string is continuously supplied to the data electrodes, in cases of display data in which the same value is continuously written to display cells, there is no need for return between data pulses to the reference potential, and there is consequently no flow of current for charging and discharging electrode electrostatic capacity and power consumption is reduced.
According to another aspect of the present invention, a plasma display device comprises a plurality of scan electrodes, a plurality of data electrode groups, a data pulse phase control circuit, and data drivers.
The data electrode groups are divisions of a plurality of data electrodes that are arranged to intersect with the scan electrodes and that realize screen display by discharge that is brought about at intersecting points with the scan electrodes upon application of a desired data pulse.
The data pulse phase control circuit creates pulse strings at different phase for each data electrode group, these pulse strings being composed of a plurality of pulses in which the start timing of a first pulse is delayed by a predetermined time and the end timing of the last pulse is advanced by a predetermined timing.
A data driver is provided for each data electrode group, and these data drivers apply to the data electrodes display data that are synchronized with the pulse strings.
According to an embodiment of the present invention, the time by which the start timing of the first data pulse is delayed is determined in advance such that the peak timing of the light emission current diverges from the peak timing of the data electrode current.
According to an embodiment of the present invention, the number of data electrode groups is the same as the number of data pulses that make up the data pulse strings.
According to an embodiment of the present invention, the time by which the start timing of the first data pulse is delayed is the same for all data electrodes, and the time by which the end timing of the last data pulse is advanced is the same for all data electrodes.
According to an embodiment of the present invention, the time of delay and the time of advancement are the same.
According to another embodiment of the present invention, a plurality of scan electrodes and a plurality of data electrodes are arranged to intersect with each other, the data electrodes are divided into K data electrode groups for 2xe2x89xa6K; and the plasma display panel is driven such that discharge is brought about at the points of intersection between scan electrodes and data electrodes upon the application of a desired data pulse to the data electrodes, and screen display is realized by this discharge.
This plasma display panel drive method successively applies scan signals of a prescribed pulse width to a plurality of scan electrodes, generates mask signals that straddle the points of change of the scan signals, and, once every K data pulses, masks data pulses with mask signals that are shifted one pulse width of a scan signal for each data electrode group. According to another embodiment of the present invention, a plasma display device comprises a plurality of scan electrodes, K data electrode groups, a scan driver, a data pulse phase control circuit, and data drivers.
The data electrode groups are divisions of a plurality of data electrodes that are arranged to intersect with the scan electrodes and that effect screen display by discharge that is brought about at intersections with the scan electrodes upon application of desired data pulses.
The scan driver successively applies scan signals to a plurality of scan electrodes at a desired pulse width.
Once every K data pulses, the data pulse phase control circuit creates mask signals in which pulses appear that straddle the points of change of the scan signals and that are shifted one pulse width of a scan signal for each data electrode group.
A data driver is provided for each data electrode group, and each data driver applies a data pulse that is masked by a mask signal to the data electrodes.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.